1. Field of the Invention
The present invention relates to a planar (i.e., two-dimensional) optical waveguide and a method of manufacturing the same.
2. Related Background Art
The quick spread of mobile phones and personal information terminals in recent years has entailed development of down-sized, lightweight and sophisticated circuit boards that are highly integrated and adapted to operate very fast. As a result, there have arisen problems including wiring delays and EMI (electromagnetic interferences).
While conventional electric wiring suffers from such problems, optical wiring technologies have drawn attention as means for dissolving the problems because optical wiring is free from wiring delays and signal degradations and can reduce electromagnetic interferences caused by wires.
For example, Japanese Patent Application Deposited-Open No. 9-96746 discloses an optical circuit board as described below, which exploits advantages of optical wiring. The disclosed optical circuit board has an optical wiring section and an electric wiring section separated from each other. Light that is transmitted through the optical waveguide arranged on the substrate is modulated by driving an optical switch or an optical modulator also arranged on the substrate by means of a voltage signal applied to it from an electronic device. In this way, an electric signal is converted into an optical signal and transmitted. Then, the optical signal is received by a light-receiving device arranged on the substrate or on some other substrate and converted back into an electric signal, which electric signal is then conveyed to some other electronic device or some other part of the same electronic device. While optical wiring is provided as supplementary means for avoiding problems of electric wiring in the optical circuit board of the above identified patent document, the area that can be used for electric/optical signal conversion or optical/electric signal conversion is limited because a linear transmission path (linear polymer waveguide) is used for the optical wiring.
Japanese Patent Application Deposited-Open No. 2000-199827 proposes the use of a mirror that is inclined by 45° relative to the light path of an optical waveguide in order to efficiently couple rays of light entering or exiting perpendicularly relative to the light path of the optical waveguide. However, the transmission path is again linear because the 45°-inclined mirror is used in order to couple an incident light beam to the optical waveguide and also a light beam transmitted through the optical waveguide to a light-receiving device. Then, the positions that can be used for arranging the light-emitting device and the light-receiving device are limited to by turn limit freedom of design particularly when a plurality of transmission paths have to be arranged.